The present invention relates to a floating seal used as a sealing device for a rotary shaft in a machine such as a construction vehicle, or other construction equipment or the like.
As shown in FIG. 1 floating seals 5, 5 are disposed at an end of a rotary shaft 1 such that they are in contact with a casing 2 and a rotary plate 3 through O-rings 4, 4 respectively, Thus, silt, dust, waste water, and the like are prevented from entering through a gap between the casing 2 and the rotary plate 3 by seal faces 6, 6 of the respective floating seals 5, 5, and the O-rings 4 and 4. The seal faces 6, 6 are required to be wear resistant since they have to relatively slide at the rotational speed of the rotary shaft 1.
Accordingly, a material which is particularly superior in wear resistance, such as alloyed cast iron, chilled cast iron, or the like, is used for the floating seal. However, such wear proof cast irons are not so good in machinability, castability and producibility, while being superior in wear resistance.
To solve this problem, there has been proposed a composite floating seal in which a wear resistant material is disposed at only the seal face at which wear resistance is required, or a floating seal in which the seal face of a base metal of steel is processed to provide wear resistance thereat by a method such as boronizing. There are questions, however, regarding the strength of the junction portion in cases where different materials are compounded. There are also disadvantages where the wear resistant surface processing is performed by a surface coating method such as metal plating, metal spraying, or the like. Where the floating seal is subject to abrasion with strong contact pressure, the coating is apt to come off. In the case where the wear resistant surface processing is performed by a method such as boronizing, ion nitriding, or the like, it is difficult to obtain a sufficiently deep hardened layer as well as difficult to obtain the necessary wear resistance even if the surface hardening processing is performed, unless the base metal of substrate per se has hardness to a certain extent.